This invention relates to a novel apparatus for separation of solids in froth as described in the preamble of appended independent patent claim.
This invention mainly pertains to froth separators used in mineral ore dressing machines. The present invention particularly refers to froth separators of the flotation type, in which pulp, pulverized ore mixed with water, is fed to the surface of a preliminary prepared froth layer. Such devices are intended for the separation of coarse grains of different minerals and materials and can be used in e.g. the metal industry, the construction materials industry or the mining industry.
A froth separation device is known from U.S. Pat. No. 4,274,949, the device including a reservoir having an inclined flat screen installed across the reservoir from one wall to the other. Froth generators are assembled inside the reservoir above the screen and several pulp feeding devices are located along the top of the separation device. Pulp is arranged to leak through the froth layer produced by froth generators. Tailings, i.e. particles which are not captured by the froth, fall through the screen and leave the reservoir together with the pulp flow. Separated froth product (captured particles and froth) leaves the process as a concentrate. The inclined screen causes the froth product to move towards an output opening on the bottom of the reservoir, through which opening the froth product is discharged. Removal of the tailings is organized through an opening in the bottom of the reservoir under the screen.
Another device for separation in froth is known from U.S. Pat. No. 4,469,591. In the device a continuously generated foam flux is transported along the outer surface of a horizontal drum, and mineral particles are deposited on the surface of the foam. Dense mineral particles fall through the foam but less dense particles stay on the upper surface of the foam. Floated particles together with the upper surface of the foam are skimmed away by blades, while the particles which passed through the foam stay on the drum and are transported away.
However, the devices described above have several shortcomings, such as low separation efficiency, the concentrate being contaminated by dirt (tailings), low stability of the dressing process due to fluctuations in the pulp feeding or froth thickness.
Further, from U.S. Pat. No. 3,815,739 is known a froth separation machine, which includes a chamber having installed therein a two layer bubble generator which is formed of perforated rubber hose pipes connected to a compressed air source. A slit-type airlift is located along the central longitudinal chamber axis. The machine is equipped with a distributor feeding device which distributes the pulp flux equally towards both sides of the machine. The device includes one chamber with a damper for pulp level adjustment and one for the coarse pulp fraction discharge. Inclined plates are placed under the bubble generators to guide the coarse sized fraction of the material down to the bottom of the chamber, where the inlet of the airlift is located. The airlift transports the material to the upper part of the machine, where this fraction is guided on to the froth surface. After the contact with the froth surface hydrophobic particles keep themselves on or in the froth and are discharged from the dressing process with the froth by mechanical froth skimmers. Hydrophilic and not floated particles fall down through the froth layer, slip down along the inclined planes, enter the airlift and are transported to the froth surface again and again.
The shortcomings of the described construction are:
the airlift in principle can not provide a stable enough feeding of the process;
high water content in the feed is needed because of the airlift use, which gives an opportunity for the hydrophobic particles in the water to slip through the froth layer,
the use of the mechanical froth skimmers destroys the froth very efficiently; this leads to extra losses of useful mineral particles, which were already captured by the froth; this affects particularly to the coarsest mineral grains which are the most important to be separated,
the machine is basically designed to work as a separate unit, and does not allow to create the flotation mineral dressing technological schemes further without additional stages of mechanical pumping for the tailings and the concentrate which will negatively affect onto the flotation efficiency.
It is also known from a British patent GB 1131649 an apparatus for separating mineral particles by a flotogravitation process.
The object of the present invention is to provide an improved apparatus for separation of solids in froth in which above mentioned shortcomings have been minimized.
The object of the present invention is also to provide an apparatus in which the efficiency of the separation of the coarse solid particles including minerals of about 1 mm size or more is improved.
The object is particularly to provide an apparatus for improved separation in froth process.
The objects presented above are fulfilled by an apparatus characterized by features mentioned in the characterizing portion of appended independent patent claim.
An typical apparatus for separation of solids in froth, according to the invention, includes
a housing, delimited by two upper side walls, two upper end walls and a mainly funnel shaped bottom, the housing establishing a chamber for flows of liquid and solid material and a froth bed on the liquid,
feeding means for getting incoming material to be separated in contact with said froth bed,
discharging means for solid material near the bottom of said housing,
aerator means under the liquid surface for creating bubbles and thus forming said froth bed on the liquid in the apparatus, said aerator means being constructed to generate a vertical flux of bubbles substantially nonhomogenous in a horizontal cross-section of the chamber, to generate a moving bed of froth on the liquid,
means for discharging froth from the housing including at least a froth outlet, and
a surface connected to said feeding means so as to reduce the vertical speed component of the material being fed with the feeding means from above said froth bed in and on to said froth bed.